Anchor bolt assemblies have been widely used for many decades in both the construction field for securing a support structure to a wall and in the mining field to achieve strengthening of a rock structure. The most commonly used anchor bolt assembly uses an expandable portion attached to a threaded stud or bolt which is placed in a bore hole formed in a wall or other hard receiving material, such as rock, concrete and the like. The anchoring operation is effected by applying a torque to a working part on the end of the stud or bolt extending from the hard receiving material so as to cause rotation of the stud or bolt and radial widening of the expandable portion into engagement with the hard receiving material. Two commonly used expandable anchor bolt assemblies include expansion dowels having an expansion sleeve and wedging portion for expanding the sleeve, and anchor bolts having a plurality of expandable segments.
A second more recent type of anchor bolt assembly uses an adhesive or grouting material within the bore hole for securing the stud or bolt in place. When the resin or grouting material has sufficiently hardened, the working part on the outer end of the bolt or stud is rotated to torque an anchoring section embedded in the grouting material.
In either the expansion anchor bolt assembly or the adhesive type anchor bolt assembly, a secure connection between the anchor bolt assembly and the hard receiving material is obviously essential to the initial and continued proper functioning of the anchor bolt assembly. In either case, a secure connection is achieved by the application of a preset torque to assure that sufficient anchoring contact with the hard receiving material is attained. In the case of the expansion anchor assembly, there is a direct relation between the torque applied to the working portion of the stud or bolt and the radial expansion of the expansion portion so that the application of a preset torque is required to assure that sufficient anchoring is provided with the materials in which the anchor bolt is set. In the case of the adhesive type anchor bolt, there is a direct relation between the proper setting of the resin and the torque applied.
A preset torque can be applied to the working part of the stud by means of a torque wrench. Such wrenches, however, are expensive and sensitive to damage. Accordingly, it has also been known to provide a second working part connected to the first working part on the stud by a shear device rated to break when a preset torque is attained. Known shear devices interconnecting the two working parts include shear pins, shear rings, or interconnections such as spot welding and the like. Each of the working parts is provided with surfaces on which a tool can be placed for applying torque to the stud. In many cases, the working surfaces are in the form of a multisided member, such as a bolthead.
Once a preset torque has been applied to the anchor bolt so that the second working part has broken away from the first working part, a secure connection between the stud and the hard receiving material is created. If, however, torque is applied directly to the first working part mounted on the stud, whether it is for detaching or further tightening of the anchor bolt assembly, it leads to a departure from the preset torque and, therefore, a change in the preset anchoring values. Even though a minor detachment takes place, it is possible that the expansion portion under load will not be able to expand again or, if additional torque is applied, the bore hole into which the sleeve is inserted may be destroyed by exceeding its breaking point with a consequent drop in the anchoring values of the bolt assembly.
Accordingly, the optimum anchoring characteristics of the bolt assembly can only be insured if, after the flangible shear device breaks upon attainment of a preset torque, no further torque is transmitted through the first working part to the stud. Until the present time, it has been known to provide a device for indicating whether a tool has been used on the first working part of the stud for applying torque above the preset value. U.S. Pat. No. 4,167,886 issued to Seghezzi et al discloses an expansion dowel assembly having an indicating device which prevents an application of torque to the stud until at least portions of the indicating device or separating member have been removed. The separating member is in the form of an annular flange with spaced fingers positioned along, and in contact with, at least one side of the first working part to prevent the effective placement of a torque applying tool on the first working part. Accordingly, torque can be applied to the first working part only after the removal of a portion of the separating device and removal of such position is easily visually recognized so that it is simple to determine whether any further torque has been applied after the second working part has been removed from its position enclosing the first working part. Therefore, it can be assumed that any break in the flange represents a removal of one of the fingers and affords an indication that additional torque has been applied.
Although the indicating device disclosed in Seghezzi et al provides a means of visually determining whether an anchor bolt assembly has been tampered with, such a device does not permanently prevent the application of additional torque to the first working part. A passerby can impair the secure connection of the anchor bolt assembly by merely removing the fingers and applying torque to the first working part. The separating member of ringers are positioned in contact with the outer surface of the first working part so that a gripping or torquing tool of some sort could be used to apply torque to the stud via the first working part by gripping the outer surface of the fingers. Also, a portion of the outer working surface of the first working part remains exposed and therefore may be engaged by a tool for applying torque.
German Patent No. 2658996 to Hilti AG discloses a mechanical torque indicator for use with an anchor type member which includes a plurality of separate parts. This unit includes an elongate pin threaded at one end with a wedge member screwed onto the threaded end of the pin. The opposite end of the elongate pin is secured to a counter bearing which retains a threaded nut, and a second short threaded pin is connected at one end to the nut and at the opposite end is threaded into a torque applying nut. To permit the torque applying nut to rotate relative to the counter bearing, a slide washer is mounted on the second short pin between the two. As the torque applying nut rotates, it causes the second short pin to draw the threaded nut axially thereby drawing the elongate pin axially to cause the wedge to move axially into a casing to spread and anchor the casing. When the axial torque on the short pin exceeds a predetermined amount, the pin will break at some point releasing the washer and the torque applying nut.
The multiple parts combined with the axial torquing of the Hilti AG patented unit prevent this unit from providing an accurate control of torque. The ability of the multiple components of the unit to shift relative to one another, even slightly, can cause torque errors, but even more significant is the fact that the application of axial torque to the uniformly shaped short pin will cause the torque to spread along the length of the pin, and each pin will ultimately break at its weakest point. With no torque concentration at a weakened point of predetermined strength, accurate torque control cannot occur, nor is the breakage point controlled to prevent injury to an operator. Once breakage occurs, this patented anchor unit cannot be effectively adjusted or released, nor is it protected from unnoticeable tampering.
Thus, there is a need for a simple and effective anchor bolt assembly for providing a secure and properly torqued connection between a stud and a supporting body while also preventing subsequent unrecognized tampering with the connection.